The present invention concerns a device for the stretching of a weft thread in weaving machines, in other words a device which is installed at the end of the shed of a weaving machine so as to catch a weft thread inserted in the shed, and so as to avoid the recoil of the weft thread at the end of the insertion, and keep it taut during the beating up.
It is known that such devices consist of a thread guide duct in which the ends of the weft threads are caught and that they are kept taut by means of an air stream in this thread guide duct. It is also known that such a device maybe attached to the sley, such that the caught thread ends, if they have a normal length, are automatically released from the thread guide duct during the return movement of the sley, as a result of which the thread guide duct is always free at the beginning of the next insertion.
If a strongly twisted weft thread is used, one should weave with a relatively long waste end, so as to make sure that the stretch effect is sufficiently great to avoid the situation in which the weft thread recoils and screws up in the shed. With such long waste ends the course of the sley is insufficient to ensure that the weft thread, after beating up against the cloth line, is released from the above-mentioned thread guide duct of the stretching device. As a result, that several threads end up in the thread guide duct of the stretching device, which may cause obstructions.
A known solution to this problem consists in using a thread guide duct with a larger diameter, but this is disadvantageous in that the consumption of air is great and in that the stretching force is relatively small.
Another known solution is described in Belgian patent No. 1.000.989, whereby use is made of an auxiliary nozzle which is fixed on the weaving machine, in particular near the cloth line of the fabric. This auxiliary nozzle is useful in case weft threads are used with a waste end of a normal length, but it is inefficient with weft threads having long waste-ends as mentioned above, because in the rearmost position of the sley the force exerted by said auxiliary nozzle on the waste end situated in the stretching nozzle is insufficient to blow this waste end out of the thread guide duct.